The use of fiber reinforced concrete (FRC) has passed from purely experimental laboratory scale applications into factory and field applications involving the placement of many thousands of cubic yards annually throughout the world.
Experience has indicated the advisability of modifying or creating new testing methods and procedures to insure reproducible meaningful results with these unique material systems. There has been an effort in the industry to standardize procedures and equipment so that results can be effectively evaluated and compared. There are adequate testing procedures for fiber reinforced concrete and the like for many properties such as the modulus of rupture, compressive strength, tensile strength, shrinkage, creep, modulus of elasticity, etc., but there is a need for a better apparatus and method for testing and indexing the impact strength of such materials.
Impact strength is an important property of fiber-reinforced concrete. It can be used to compare the relative merits of different fiber concrete mixes or to demonstrate the improved performance of a fiber mix when compared to a conventional concrete mix. It can also be adapted, if desired, to show the relative impact resistance of different thicknesses of material.
One of the major material properties of fibrous concrete is its tremendous impact resistance when compared to conventional concrete. There are only a couple of methods that are presently available for testing or analyzing any material for impact and these are not useful for concrete, for example the Charpy and Izod tests. The Charpy equipment uses a large swinging pendulum which strikes a notched test specimen. The distance that the pendulum travels after breaking the specimen is a measure of impact resistance. This equipment is not applicable to concrete since very large samples would be required. The equipment is expensive, heavy, large, non-portable and requires a rigid base for mounting. The Izod method has been used in Europe for evaluating impact resistance and it involves subjecting a test specimen to an impact load after which its internal micro-cracking is analyzed with ultrasonic sound wave equipment and an oscilloscope. Neither of these methods are practical, economical, or portable and the latter test requires technicians which are highly trained. Consequently, there is a need for a method and apparatus of testing impact strength to overcome these disadvantages.